1. Field of the Invention
The present invention relates to a prism sheet for use in, for example, a backlight module, the backlight module typically being employed in a liquid crystal display (LCD).
2. Discussion of the Related Art
In a liquid crystal display device (LCD device), liquid crystal is a substance that does not itself illuminate light. Instead, the liquid crystal relies on light received from a light source to display information. In the case of a typical liquid crystal display device, a backlight module powered by electricity supplies the needed light.
FIG. 8 represents a typical direct type backlight module 100. The backlight module 100 includes a housing 11, a plurality of lamps 12 positioned above a base of the housing 11 for emitting light, and a light diffusion plate 13 and a prism sheet 10 stacked on top of the housing 11 in that order. Inside walls of the housing 11 are configured for reflecting certain of the light upwards. The light diffusion plate 13 includes a plurality of dispersion particles (not shown) therein. The dispersion particles are configured for scattering light, and thereby enhancing an uniformity of light exiting the light diffusion plate 13.
Referring to FIG. 9, the prism sheet 10 includes a base layer 101 and a prism layer 102 formed on the base layer 101. The prism layer 102 contains a plurality of parallel prism lenses 103 having a triangular cross section. The prism lenses 103 are configured for collimating received light to a certain extent. Typically, a method of manufacturing the prism sheet 10 includes following steps. First, an ultraviolet cured transparent melted resin is coated on the base layer 101, and then the ultraviolet cured transparent melted resin is solidified to form the prism lenses 103.
In use, light from the lamps 12 enters the prism sheet 10 and becomes scattered. Thus, scattered light leaves the light diffusion plate 13 to the prism sheet 10. The scattered light then travels through the prism sheet 10 and is refracted out at the prism lenses 103 of the prism sheet 10. Thus, the refracted light leaving the prism sheet 10 is concentrated by the prism lenses 103 and increases a brightness (illumination) of the prism sheet 10. The refracted light then propagates into an LCD panel (not shown) positioned above the prism sheet 10.
When the light is scattered at the light diffusion plate 13, scattered light enters the prism sheet at different angles of incidence. Referring to FIG. 10, when scattered light generally travels through the prism sheet 10 at different angles of incidence, the scattered light generally travels through the prism sheet 10 along three light paths. A first light path the prism lenses 103 at angles closer to normal of the base layer. A second light path (such prism lenses 103 at angles closer to normal of an outer surface of the prism lenses 103. Both the first light path and the second light path increases light utilization efficiency of the backlight model. However, a third light path (such as a5, a6) enters the prism sheets at certain angles such that when leaving the light prism sheet at the prism lenses 103, light undergoes internal reflection at the prism lenses 103, or re-enters the prism sheet 10 at an outer surface of adjacent prism lenses. Thus, light traveling along the third light path will eventually exit the prism sheet at the same side the light enters. The third light path does not contribute to the light utilization efficiency of the backlight module 100. Furthermore, the third light path of light is consumed in interface propagation, insulting decreasing a brightness of the backlight module 100.
What is needed, therefore, is a new prism sheet and a backlight module using the prism sheet that can overcome the above-mentioned shortcomings.